1. Field of the Invention
The present invention is directed to a control circuit for an electro-therapy device, i.e. a device for administering medical treatment to a patient in the form of electrical energy, such as an RF surgery device, and in particular to such an electro-therapy device having at least one electrode carrying a high voltage for delivery to a patient and at least one switch connected to the electrode.
2. Description of Prior Art
In conventional electro-therapy devices, a treatment electrode is structurally combined with at least one switch, for example at or in a handle which is used to manipulate the treatment electrode. The switch gives the user, i.e. the person administering the treatment, the possibility of immediately influencing the operation of the electro-therapy device. In the simplest case, the switch controls an on-off function. For safety reasons, especially to protect the person to be treated from the high voltage of the electrode, the switch is generally physically separated from the source of voltage potential and from the ground for the electro-therapy device. Such electrodes are usually exposed to rugged operating conditions, for example, out of doors when resuscitating cardiac activity with electrical shocks (stimulation currents), or in operating room when manipulating in or at surgical wounds. In any case, the risk is present that moisture, for example rain in the out of doors or body fluid in the operating room, can proceed to the switch at the electrode. Such fluid may create new current paths to the high voltage, or may short circuit existing current paths, which may not only result in a deterioration of the electro-therapy device, but also jeopardizes the safety of the person to be treated.
It is also a desirable feature of such electro-therapy devices that the electrode be easy to manipulate. Usually the electrode will include more than one switch associated therewith. The rugged operating conditions, particularly the actions of moisture, require a high outlay for insulation between the switch and the electrode, given the high voltages which are present at the electrode. If such a handle were constructed, it would be too large and too heavy to easily manipulate. This disadvantage could be avoided, in theory, if the effective insulation between the switch and the high voltage of the electrode were displaced into the electro-therapy device itself (i.e., out of the handle). If this were done, however, a multitude of components which are electrically connected to the switch, for example relays and components for generating the operating voltage, must then be heavily insulated.
A circuit for controlling a RF surgery device is disclosed in German AS 24 57 900. In this known device, a filter tuned to the frequency of a low-frequency auxiliary signal contains a transformer for voltaically separating the potentials. In combination with a resonant capacitor, the primary side of the transformer forms the emitter resistor of a transistor switching stage connected thereto. Under the resonant condition, the filter has a high impedance which causes the switching transistor to be non-conducting. The secondary side of the filter also contains a resonant capacitor, which can be shorted by a switch connected thereto. When the switch is actuated, the resonant condition is no longer present, i.e. the filter is detuned, which causes the impedance at the primary side of the filter to drop, and the switching transistor becomes conductive, as a result of which the RF generator is switched. This control circuit, therefore, requires an additional frequency filter, which must be insulated, for each switch which is provided.
A circuit is disclosed in German OS 24 57 221 for selecting types of current in a RF surgery device which includes an electrode handle having a two-poled switching arrangement with two actuators, so that different current levels can be delivered to a patient by respectively depressing one or both of the actuators. The handle is remote from a housing of the surgery device. A blocking stage disposed in the housing provides the only means for electrically connecting the components of the handle to the components in the housing. The housing also contains a high-frequency current source, a transformer, and control circuitry. The control circuitry and the blocking stage are connected to the secondary of a transformer which supplies a low-frequency a.c. voltage to the control circuitry. The control circuitry includes two relays and two diodes respectively connected in series therewith, the diodes being connected with opposite polarity. Each relay is bridged by a capacitor. The blocking stage permits direct current to pass therethrough, but blocks high-frequency current. The blocking stage is a pentapole consisting of two chokes and three capacitors. Again, a relatively high outlay for electrical insulation is required at these components.